1. Field of the Invention
The invention relates generally to the field of electrical and optical cables. More specifically, the invention relates to such cables made with impregnated fiber strength layers.
2. Background Art
Electrical and optical cables known in the art include one or more conductors, typically covered by a layer of insulating material such as plastic. An electrical cable may include a conductor that electrically conductive, and an optical cable may include a optical fiber that conducts an optical signal. In an optical cable, one or more optical fibers may be enclosed in a plastic or metal tube for protection. The foregoing structures may be enclosed in or associated with a strength member for providing the cable with the capacity to withstand axial tension. The strength member may be internal to the cable and include various forms of braided or wound material such as steel wire, natural fiber or man-made fiber, wherein the cable is covered on its exterior by a jacket such as may be made from plastic. The strength member may also be external to the cable, such as a plurality of coaxial, contrahelically wound layers of steel wire surrounding the foregoing electrical conductors and/or optical fibers. Such external armor may provide the cable with substantial axial load carrying capacity and protect the foregoing structures from damaged caused by abrasion. The most common configuration for the foregoing types of cables is round, wherein the cable has a substantially circular cross-section. The foregoing round cables have been used successfully in harsh environments, including placement in subsurface wellbores having high fluid pressure, chemically active fluid, and high temperature.
Other types of cables may be flat, having a substantially rectangular cross-section and including a plurality of electrical conductors and/or optical fibers arranged side by side and enclosed in a plastic jacket or deposited on a plastic substrate. Such cables are commonly known as “ribbon cables” and may be used for purposes such as making electrical connection from control circuits to a printer head in a computer printer. Other uses for such ribbon cables include open waveguides, such as widely familiar 300 ohm impedance analog television signal transmission cable. See, for example, U.S. Pat. No. 6,015,607 issued to Fraivillig.
For all of the foregoing types of cable, the plastic used for insulation and fluid exclusion is typically a flexible plastic material that may be extruded or similarly formed into suitable shapes. Such plastic material includes, for example, polyethylene, neoprene, nitrile rubber, and a material sold under the trademark TEFLON, which is a registered trademark of E.I. DuPont de Nemours & Co. Wilmington, Del.
Plastic impregnated fiber perform is used to make articles such as fluid carrying tubes and liners for metal fluid carrying tubes. See, for example, U.S. Pat. No. 7,114,751 issued to Reynolds. Plastic impregnated fiber perform may include a fiber, such as glass fiber, graphite fiber, or synthetic polymer fiber such as aramid fiber, formed into a selected pattern, such as a braided sleeve or sheet. The fiber formed in the selected pattern is then impregnated with plastic material, such as thermoplastic or chemically cured resin such as epoxy resin. The plastic or resin upon cure causes the fiber perform to make a structure that is resistant to chemical attack, can withstand fluid under pressure, and typically has substantial mechanical strength, such as to resist fluid intrusion and carry axial loading.
There continues to be a need for electrical and optical cables that can withstand harsh environmental conditions and can have substantial mechanical strength.